Use of fluorinated polyurethanes for the treatment of films or sheets made of cellulose, graphite, mica, kaolin, leather and similar natural materials

ABSTRACT

A class of cross-linked fluorinated polyurethanes, which can be used for protecting and reinforcing coatings on films, sheets, laminates and similar thin structures made of cellulose, graphite, mica, kaolin, leather etc. as well as for adhesive and reinforcing material in multi-layer structures made of films, sheets, laminates and similar thin structures made of graphite, mica, kaolin, etc. These polyurethanes can be obtained starting from the following components: 
     (A) a polyisocyanate consisting of a perfluoropolyether chain bound to the --NCO terminal groups through an aromatic or cycloaliphatic radical; and 
     (B) a polyol consisting of a perfluoropolyether chain bound to the --OH terminal groups through an aromatic or cycloaliphatic radical.

BACKGROUND OF THE INVENTION

This invention relates to the use of fluorinated polyurethanes, endowedwith a particular combination of properties, for the treatment of films,sheets and similar thin structures made of natural materials such ascellulose, graphite, mica, leather and kaolin.

Fluorinated polyurethanes containing polyoxyperfluoro alkylenic blocksalternating with hydrogenated rigid segments are disclosed in ItalianPatent No. 903,446, U.S. Pat. No. 4,782,130 and European PatentApplications No. 359,272 and 359,273.

Said polyurethanes are used as elastomers for tightness systems employedin very hard operating conditions, characterized by an aggressiveenvironment and with very low temperatures.

The principal aim of the above Italian Patent No. 903,446 is thesynthesis of perfluoropolyether prepolymers containing hydroxyl terminalgroups for the preparation of cross-linked polyurethanes, endowed with avery low Tg. Suitable polyisocyanates are the conventional hydrogenatedaliphatic, or aromatic ones and the fluorinated aliphatic ones.

When the above said isocyanates are employed, problems of homogeneityduring the synthesis are often encountered. Moreover, the structuresdisclosed in the above Italian Patent do not allow to obtain productsendowed with sufficient mechanical properties. In particular, thetensile strength is usually less than 1 MPa.

The aim of the other three above mentioned documents is the obtainmentof materials having improved mechanical properties. This is obtained bymeans of a block structure constituted of flexible blocks ofperfluoropolyether chains and rigid segments constituted of ahydrogenated diol or polyol, an hydrogenated diisocyanate and,optionally, an hydrogenated diamine.

The thus obtained polyurethanes are elastomers having a high elasticmodulus and, therefore, endowed with a quite high rigidity, which isuseful in some application but undesired in others. In the preparationof these polyurethanes, in view of the contemporary presence offluorinated prepolymers and hydrogenated monomers having low reciprocalcompatibilities, it is necessary to use mixtures of particular solvents,one of which is a solvent of the fluorinated substances and the other ofthe hydrogenated ones.

SUMMARY OF THE INVENTION

It has now been found that a particular class of fluorinatedpolyurethanes shows a combination of properties which renders themparticularly suitable for the above described utilization.

Said properties comprise:

an excellent elasticity even at very low temperatures, due to a very lowTg, usually lower than -100° C.;

a very good combination of mechanical properties in view of the abovedescribed utilization and, particularly, high tensile strength andelongation at break together with not too high hardness and elasticmodulus, so that the polymer is endowed with a very good flexibilitytogether with a high mechanical strength;

very good chemical resistance, in particular toward acids, bases,oxidants, solvents, water and steam;

very good film-making and adhesive properties;

excellent dielectric properties;

absence of residual tackiness.

Therefore, an object of the present invention is to provide a class offluorinated polyurethanes endowed with the above described optimalcombination of properties for their utilization as protective andreinforcing coatings on films, sheets, laminates and similar thinstructures made of cellulose, graphite, mica, kaolin, leather andsimilar natural materials which are fragile and/or sensitive to externalagents, and for their utilization as adhesive and reinforcing materialfor multi-layer structures made of films, sheets, laminates and similarthin structures made of graphite, mica, kaolin and similar fragilenatural materials.

DETAILED DESCRIPTION OF THE INVENTION

This and still other objects are obtained by employing fluorinatedpolyurethanes obtainable starting from the following components:

(A) at least one fluorinated diisocyanate or polyisocyanate, havingnumber average molecular weight ranging from 500 to 7000, of thefollowing formula:

    [(OCN).sub.n R].sub.z --(Z.sup.1).sub.d --[R(NCO).sub.q ].sub.z(I)

wherein Z¹ is a bivalent or trivalent radical selected from the groupconsisting of --CONH--, --CH₂ --, --CH₂ O--, CH₂ OCH₂ --, --O--, --CH₂OSO₂ --, --CH₂ O--CONH, --CH₂ O(CH₂ CH₂ O)_(b) --, H₂ O(CH₂ CH₂ O)_(b)--CO--NH-- (wherein b is an integer ranging from 1 to 10, and preferablyfrom 1 to 3), ##STR1## (wherein R³ and R⁴, same or different, are alkylradicals having from 1 to 4 carbon atoms), ##STR2## R is a divalent orpolyvalent aromatic or cycloaliphatic radical having from 6 to 20 carbonatoms; provided that when Z¹ is the radical ##STR3## it can only bebound to an aromatic radical; d is 0 or 1;

z is 1 when d is 0 or when Z¹ is a divalent radical, and is 2 when Z¹ isa trivalent radical;

(n·z) and (q·z), same or different, are integers ranging from 0 to 2;

(n·z)+(q·z) is an integer ranging from 2 to 4;

Q is a perfluoropolyether or fluoropolyether chain selected from thegroup consisting of:

    (1°)--CF.sub.2 --O--(C.sub.2 F.sub.4 O).sub.m (CF.sub.2 O).sub.p --CF.sub.2 --                                             (II)

wherein the (C₂ F₄ O) and (CF₂ O) units are randomly distributed alongthe chain and m/p ranges from 0.2 to 2;

    (2°)--CF.sub.2 --CH.sub.2 --(OCF.sub.2 --CF.sub.2 --CH.sub.2).sub.r --O--R.sup.1 --O--(CH.sub.2 --CF.sub.2 --CF.sub.2 O).sub.s --CH.sub.2 --CF.sub.2 --                                             (III)

wherein R¹ is a fluoroalkylenic radical containing from 1 to 10 carbonatoms and r/s ranges from 0.8 to 1.2; ##STR4## wherein the units##STR5## (C₂ F₄ O) and (CFXO) are randomly distributed along the chain,X is F or CF₃, t/u ranges from 0.6 to 2.0, u/v is higher than 10;##STR6## wherein R² is a perfluoroalkylenic radical containing from 1 to10 carbon atoms, and c/f ranges from 0.8 to 1.2; and

(B) at least one fluorinated diol or polyol, having number averagemolecular weight ranging from 400 to 7000, of the following formula:

    (HO).sub.n,R--(Z.sup.2).sub.d --(Z.sup.3).sub.d --Q--(Z.sup.3).sub.d --(Z.sup.2).sub.d --R(OH).sub.q,                          (VI)

wherein Z² and Z³, same or different, are bivalent radicals selectedfrom the group consisting of --CONH--, --CH₂ --, CH₂ O--, --CH₂ OCH₂ --,--O--, --CH₂ OSO₂ --, --CH₂ O--CONH--, --CH₂ (OCH₂ CH₂)_(g) -- (whereing is an integer ranging from 1 to 10, and preferably from 1 to 3),##STR7## (wherein R³ and R⁴, same or different, are alkyl radicalshaving from 1 to 4 carbon atoms),

or Z² and Z³ together represent the radical --CHOH--CH₂ OCH₂ --; R, Qand d have the above indicated meaning;

n' and q', same or different, are integers ranging from 0 to 2;

n'+and q' has a value ranging from 2 to 4;

(n·z) (of component A)+(q·z) (of component A)+n'+q' has a value rangingfrom 5 to 8, and preferably of at least 6.

These new fluorinated polyurethanes are endowed with a cross-linkedstructure as result from the fact that the sum of the indexes(n·z)+(q·z)+n'+q' has a value ranging from 5to8.

Fluorinated diisocyanates and polyisocyanates of formula (I) are per seknown. In particular, said compounds, together with the method for theirpreparation starting from alcohols, acids, esters and acyl halides, aredisclosed in the U.S. Pat. No. 4,094,911.

Fluorinated diols and polyols having formula (VI) are per se known aswell. In particular, said compounds and the method for their preparationare disclosed in the above mentioned Italian Patent No. 903,446.

The fluorinated polyurethanes utilized in the present invention commonlycomprise only one fluorinated di- or polyisocyanate or only onefluorinated diol or polyol.

The fluorinated polyurethanes utilized in the present invention areendowed with the above described combination of properties that makesthem particularly suitable for their utilization as protective andreinforcing coatings of films, sheets, laminates and similar thinstructures made of mica, graphite, paper, kaolin, leather and similarnatural materials which are fragile and/or sensitive to external agents,and for their utilization as adhesive and reinforcing material formulti-layer structures made of mica, graphite, kaolin and similarfragile natural materials.

In the starting polyisocyanates and polyols the R radical is divalent orpolyvalent. When it is polyvalent, it is preferably trivalent.

Among preferred R radicals, the following may be cited: ##STR8##

The possible free valences of R radicals, namely those which are notbound to Z¹, Z² or Z³ radicals or to functional group --NCO or --OH, arebound to hydrogen atoms. In the perfluoropolyether chain of formula(II), the m/p ratio is preferably comprised between 0.5 and 1.2.

In the fluoropolyether chain of formula (III), R¹ is preferably afluoroalkylene radical containing from 1 to 4 carbon atoms.

In the perfluoropolyether chain of formula (V) , R² is preferably aperfluoroalkylenic radical containing from 1 to 4 carbon atoms.

The preparation of the fluorinated polyurethane is performed directly onthe material to be coated. The two components are mixed and spread onthe material by means of conventional techniques such as, for instance,coating with pitch, sputtering or immersion of the material in themixture of the two components. The reaction may be performed without theemployment of a catalyst, for instance by heating at 100°-150° C. for atime of 2-24 hours. The employ of a catalytic system permits to operateat lower temperatures, for instance at 20°-80° C., and for shortertimes. Catalysts which may be employed are those commonly used in thepreparation of polyurethanes. Examples of said catalysts are tincomplexes, such as tin dibutyl dilaurate, iron complexes, such as ironacetylacetonate, and tertiary amines.

The equivalent ratio NCO/OH in the starting mixture has a value whichusually ranges from 1.00 to 1.05. Preferably, said ratio is 1.00.

The fluorinated polyurethanes used in the present invention may beemployed to obtain protective and reinforcing coatings or as adhesiveand reinforcing material for multi-layer structures. In particular, saidpolyurethanes can drastically improve the mechanical resistance andreduce crackings due to bendings and other stresses in thin expandedgraphite or mica sheets, therefore allowing an easier workability.

In fact, it is known that thin graphite sheets (having thickness evenlower than 0.3 mm) are obtained by hot sintering, by calenderingexpanded graphite particles. However, the material obtained by saidworking system, while endowed with very good thermic inertness, has aninsufficient resistance toward mechanical solicitations as well astoward chemical oxidants.

Therefore, in the preparation of graphite packings having a complexshape, a breaking of the packing is not infrequent.

Said drawbacks can be overcome by means of the utilization of thepolyurethanes of the present invention.

Similar problems are encountered for mica sheets that find a largeutilization where it is requested a combination of properties of thermaland electrical insulation together with the feasibility of molded or cutpieces with an extremely accurate dimensional control.

Said drawbacks too can be overcome by means of the polyurethanes of thepresent invention.

Furthermore, in a lot of applications, special products made of mica("built-up mica") are employed, which are constituted of sheets orplates (tables) made of superposed layers of mica alterned with asuitable polymeric binder by means of a process under heat and pressure

Also in this case, the use of the polyurethane binders of the presentinvention, having very good dielectric, flexibility and adheringproperties, results particularly advantageous.

In the preparation of special paper (cellulose) sheets, the need toimprove resistance to external agents, such as water, steam, greases,oils and chemical agents in general, is not infrequent.

In the known art, superficial treatments with materials having a barriereffect are described. In particular, the use of waxes or parafinesapplied in their melted form is described. Furthermore, the use isdescribed of polymers such as polyethylene which, even giving moreflexible films than those obtained with waxes and parafines, in someutilization show insufficient elasticity at low temperatures and lowresistance to solvents.

The following examples are supplied for purely illustrative and notlimiting purpose.

EXAMPLE 1

50 g of component (A) of formula (VII) having equivalent weight of 1219,corresponding to 41 meq of NCO, were fed in a 250 ml flask equipped withmechanical stirrer. Afterwards, 22 g of component (B) of formula (VIII)having equivalent weight of 537, corresponding to 41 meq of OH, wereadded under stirring. The vessel was kept under stirring for 2 minutesat 60° C. under vacuum. Then its contents was transferred in a mold andthe polymerization was completed in a mould at 130° C. for 7 hours.

Component (A) has the formula: ##STR9## wherein Q¹ is aperfluoropolyether chain according to formula (II) with m/p ratio of 1.0and numeric average molecular weight of 2000.

Component (B) has the formula:

    Q.sup.1 --(CH.sub.2 OCH.sub.2 --CHOH--CH.sub.2 OH).sub.2   (VIII)

wherein Q¹ has the above said meaning.

The thus obtained sheet has been characterized mechanically andchemical/physically. The results are the following:

    ______________________________________                                        Hardness (Shore A)    39                                                      (ASTM D2240)                                                                  Brittle point         -114° C.                                         (ASTM D746)                                                                   Elongation at break at 23° C.                                                                337%                                                    (ASTM D1708)                                                                  20% modulus at 23° C.                                                                        17.5 Kg/cm.sup.2                                        (ASTM D1708)                                                                  100% modulus at 23° C.                                                                       8.0 Kg/cm.sup.2                                         (ASTM D1708)                                                                  Tensile strenght at 23° C.                                                                   38 Kg/cm.sup.2                                          (ASTM D1708)                                                                  Contact angle with water                                                                            92°                                              (at room temperature)                                                         Contact angle with hexadecane                                                                       55°                                              Volume resistivity    >10.sup.13 Ohm. cm                                      (ASTM D257)                                                                   Dielectric rigidity   26.4 KV/mm                                              (ASTM D149)                                                                   Dielectric constant   4.4                                                     (ASTM D150)                                                                   Specific weight       1.722                                                   ______________________________________                                    

The same polymer is applied on an expanded graphite sheet havingthickness of 0.3 mm by means of film-spreading bar during the "pot life"period, that is when the viscosity of the system (lower than 10,000 cSt)allows its application.

The polymeric film is completely polymerized in stove at 150° C. for anhour, obtaining a coating whose thickness is 25 micron.

Three points flexion tests according to ASTMD790 have been carried outon the treated sheet and on the non-treated one. A maximum stress of0.40 and 0.22N respectively was observed.

EXAMPLE 2

50 g of component (A) of formula (IX) having equivalent weight of 1174,corresponding to 43 meq of NCO, have been reacted with 23.1 g ofcomponent (B) of formula (VIII) (see example 1) having equivalent weightof 537, corresponding to 43 meq of OH.

Component (A) has the formula: ##STR10## wherein Q¹ has the same meaningas indicated in Example 1.

The vessel was kept under stirring for 2 minutes at 60° C. under vacuum.Then its contents was transferred in a mould and the polymerization wascompleted in a press at 130° C. for 7 hours.

The thus obtained elastomer has the following characteristics:

    ______________________________________                                        Hardness (Shore A)     41                                                     Brittle point          -113° C.                                        Elongation at break at 23° C.                                                                 350%                                                   20% modulus at 23° C.                                                                         19.0 Kg/cm.sup.2                                       100% modulus at 23° C.                                                                        9.1 Kg/cm.sup.2                                        Tensile strenght at 23° C.                                                                    41.2 Kg/cm.sup.2                                       Contact angle with water                                                                             94°                                             Contact angle with hexadecane                                                                        61°                                             ______________________________________                                    

Following the procedure of Example 1, the polymer is applied on micasheets having thickness of 0.05 mm.

The polymeric film is completely polymerized in stove at 130° C. for 7hours, obtaining a coating whose thickness is 20 micron. A material isobtained which has improved resistance to mechanical stresses,particularly to bending.

A similar deposition was made on a paper sheet having thickness of about0.1 mm. In order to accelerate the polymerization and to reduce thetemperature, 100 ppm of tin dibutyl dilaurate (referred to the mixtureof diisocyanate and polyol) was added. Thus, after 5 hours at 80° C. thepolymerization of the coating was complete.

A sample of the so treated paper, a reference non-protected sample andanother reference sample treated with a siliconic coating, are treatedwith H₂ SO₄ at 96%. The first sample, after 20 minutes, shows only aslight swelling, while the other two samples underwent a total attack ofthe paper which is completely dissolved from the acid action. A similarresult was achieved after 20 minutes of treatment with NaOH at 50%.

Finally, a treatment in H₂ SO₄ at 3% at 20° C. for 48 hours showed thatthe paper protected with the fluorinated coating resulted unaltered. Onthe contrary, a reference non-treated sample underwent a total attackwith further total dissolution, giving rise to a cellulosic suspension.

EXAMPLE 3

40 g of component (A) having the following formula: ##STR11## wherein Q¹has the same meaning as in example 1, having equivalent weight of 1202,corresponding to 66 meq of NCO, was reacted with 71 g of diol of theformula:

    Q.sup.1 --(CH.sub.2 OCH.sub.2 --CH.sub.2 OH).sub.2         (XI)

wherein Q¹ has the same meaning of example 1, having equivalent weightof 1075, corresponding to 66 meq of OH.

The mixture of polyisocyanate and diol was spreaded on a graphite sheethaving thickness of 0.3 mm and the sheet was heated in stove at 100° C.for 2 hours. A polymeric coating is obtained having thickness of 20micron. The obtained elastic film has elongation at break of 250%, verygood adhesion properties (100% cross cut test, according to ASTMD3359)and is resistent to hydrolysis.

What is claimed is:
 1. A method for the preparation of a protectivecoating on films, sheets or laminates made of cellulose, graphite, mica,kaolin, or leather, said method comprising forming as the coating afluorinated polyurethane which is obtained by combining the followingcomponents:(A) at least one fluorinated diisocyanate or polyisocyanate,having number average molecular weight ranging from 500 to 7000, of thefollowing formula:

    [(OCN).sub.n R].sub.z --(Z.sup.1).sub.d --Q--(Z.sup.1).sub.d --[R(NCO).sub.q ].sub.z                                   (I)

wherein Z¹ is a divalent or trivalent radical selected from the groupconsisting of --CONH--, --CH₂ --, --CH₂ O--, --CH₂ OCH₂ --, --O--, --CH₂OSO₂ --, --CH₂ O--CONH--, --CH₂ O(CH₂ CH₂ O)_(b) --, --CH₂ O(CH₂ CH₂O)_(b) --CO--HN--(wherein b is an integer ranging from 1 to 10),##STR12## (wherein R³ and R⁴, same or different, are alkyl radicalshaving from 1 to 4 carbon atoms), ##STR13## R is a divalent orpolyvalent aromatic or cyctoaliphatic radical having from 6 to 20 carbonatoms; provided that when Z¹ is the radical ##STR14## it can only bebound to an aromatic radical; d is 0 or 1; z is 1 when d is 0 or when Z¹is a bivalent radical, and is 2 when Z¹ is a trivalent radical; (n·z)and (q·z), same or different, are integers ranging from 0 to 2;(n·z)+(q·z) is an integer ranging from 2 to 4; Q is a perfluoropolyetheror fluoropolyether chain selected from the group consisting of:

    (1°)--CF.sub.2 --O--(C.sub.2 F.sub.4 O).sub.m (CF.sub.2 O ).sub.p --CF.sub.2 --                                             (II)

wherein the (C₂ F₄ O) and (CF₂ O) units are randomly distributed alongthe chain and m/p ranges from 0.2 to 2;

    (2°)--CF.sub.2 --CH.sub.2 --(OCF.sub.2 --CF.sub.1 --CH.sub.2).sub.r --O--R.sup.1 --O--(CH.sub.2 --CF.sub.2 CF.sub.2 O).sub.s --CH.sub.2 --CF.sub.2 --                                             (III)

wherein R¹ is a fluoroalkylenic radical containing from 1 to 10 carbonatoms and r/s ranges from 0.8 to 1.2; ##STR15## wherein the units##STR16## (C₂ F₄ O) and (CFXO) are randomly distributed along the chain;X is F or CF₃, t/u ranges from 0.6 to 2.0, u/v is higher than 10; and##STR17## wherein R² is a perfluoroalkylenic radical containing from 1to 10 carbon atoms, and c/f ranges from 0.8 to 1.2; and (B) at least onefluorinated diol or polyol, having number average molecular weightranging from 400 to 7000, of the following formula:

    (HO).sub.n, R--(Z.sup.2).sub.d --(Z.sup.3).sub.d --Q--(Z.sup.6).sub.d --(Z.sup.2).sub.d --R(OH).sub.q,                          (VI)

wherein Z² and Z³, same or different are divalent radicals selected fromthe group consisting of --CONH--, --CH₂ --, --CH₂ O--, --CH₂ OCH₂ --,--O--, --CH₂ OSO₂ --, --CH₂ O--CONH--, --CH₂ (OCH₂ CH₂)_(g) --(wherein gis an integer ranging from 1 to 10), and ##STR18## (wherein R³ and R⁴,same or different, are alkyl radicals having from 1 to 4 carbon atoms),or Z² and Z³ together represent the radical --CHOH--CH₂ OCH₂ --; R, Qand d have the above indicated meaning; n' and q', same or different,are integers ranging from 0 to 2; n'+q' has a value ranging from 2 to 4;(n·z) (of component A)+(q·z) (of component A)+n'+q' has a value rangingfrom 5 to
 8. 2. The method according to claim 1, wherein the radical Ris selected from the group consisting of: ##STR19##
 3. The methodaccording to claim 1, wherein a mixture of said components (A) and (B)is polymerized on said films, sheets or laminates.
 4. A method for thepreparation of a reinforced multi-layer structure made of films, sheets,or laminates made of graphite, mica, or kaolin, said method comprisingforming as an adhesive and reinforcing material for said multi-layerstructure a fluorinated polyurethane which is obtained by combiningcomponents (A) and (B) of claim
 1. 5. The method according to claim 4,wherein the radical R is selected from the group consisting of:##STR20##
 6. The method according to claim 4, wherein said multi-layerstructure is prepared by placing a mixture of the components (A) and (B)between each of the layers of said multi-layer structure and allowingsaid mixture to polymerize in situ.